The present invention pertains generally to a driving device for a rotary member. In particular, the present invention pertains to a driving device for a rotary member which is used, for example, in driving a decorative rotary member of a mantel clock.
Mantel clocks having a decorative rotary member are known in the art. A decorative rotary member is provided to enhance the ornamentation of the clock. Generally, this decorative rotary member is attached to a vertical output shaft which is rotatable in a horizontal plane. Various mechanisms are known for reciprocatively rotating the decorative rotary member.
A first type of conventional mechanism uses a motor which is rotatable in only one direction to rotate the decorative rotary member via a reduction wheel train. To reciprocatively rotate the decorative rotary member, a sector gear is provided which is engaged with the wheel train. An arm is integrally connected on the sector gear, and a pair of pins is disposed within the swingable range of the arm so that when the distal end of the arm strikes against either pin, the resulting reaction reverses the rotational direction of the decorative member. An example of this mechanism is disclosed, for example, in Japanese Utility Model Laid-Open No. 59-62589 and Japanese Utility Model Publication No. 63-44767.
Another type of conventional mechanism for reciprocatively rotating a decorative rotary member is disclosed, for example, in Japanese Utility Model Publication No. 60-21821. The mechanism disclosed utilizes a temp motor of a transistorized clock. An output shaft of the temp motor is supported so as to be rotated via a hair spring, so that the decorative rotary member is smoothly rotated in a motion which conforms to a sine curve by virtue of the hair spring, thereby exhibiting graceful motion.
In accordance with the first type of conventional mechanism for rotating the decorative rotary member, the direction of rotation of the motor is reversed by mechanical means thereby making it difficult to smoothly vary the rotation speed of the rotational shaft. Therefore, the motion of the decorative rotary member is awkward and is not graceful. On the other hand, in accordance with the second type of conventional mechanism, the decorative rotary member is rotated via the hair spring, which makes its motion graceful. However, the spring constant of the hair spring must be determined, taking into consideration the mass, rotation angle and rotational period of the decorative rotary member. This complicates the design and manufacture of the mechanism, requiring an increased number of parts and increasing the cost. Furthermore, since the temp mechanism which acts as a driving source is formed by arranging permanent magnets and coils alternately with given gaps, the overall thickness of the mechanism is relatively large, which is disadvantageous to the design of a mantel clock having a decorative rotary member.